libceph: Use u32 for non-negative values in ceph_monmap_decode()

Overview

In the Linux kernel, the following vulnerability has been resolved:

libceph: Use u32 for non-negative values in ceph_monmap_decode()

This patch fixes unnecessary implicit conversions that change signedness of blob_len and num_mon in ceph_monmap_decode(). Currently blob_len and num_mon are (signed) int variables. They are used to hold values that are always non-negative and get assigned in ceph_decode_32_safe(), which is meant to assign u32 values. Both variables are subsequently used as unsigned values, and the value of num_mon is further assigned to monmap->num_mon, which is of type u32. Therefore, both variables should be of type u32. This is especially relevant for num_mon. If the value read from the incoming message is very large, it is interpreted as a negative value, and the check for num_mon > CEPH_MAX_MON does not catch it. This leads to the attempt to allocate a very large chunk of memory for monmap, which will most likely fail. In this case, an unnecessary attempt to allocate memory is performed, and -ENOMEM is returned instead of -EINVAL.

Affected

• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < ee5588e2bc41acb73f6676c0520420c107cd0140
• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < 86f7060cd638d6eb042e8ed780fb83a59ca0dcb3
• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < 5f2806684b05bd24d05c091083b8e2517ba8ffac
• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < b268984ae88cb0dcd7a8e8263962c748448e26e8
• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < ba0a4df8c563536857dcbf7b4dbd0f2a15f57ace
• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < 08bc6173fd611ad5a40f472bf5f15b92aea0fe40
• Linux >= a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c < 770444611f047dbfd4517ec0bc1b179d40c2f346
• Linux 5.11

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.